Telephone transmitter



Aug. 19, 1952 H. w. BRYANT TELEPHONE TRANSMITTER Filed Dec. 1, 1950 FACE -u/ INVEN 70/? H. W. BRYANT A TTORNEV VERTICAL FACE-DOWN 4 5 4 R rm 0 F 3 w u y u v, w z a u a m 4 y 2 w M m F n.L n I n n V \0 m 0 w w w G H $3 E25. MR3

Patented Aug. 19, 1952 UNITED STATES PATENT TELEPHONE TRANSMITTER Herbert W. Bryant, Chatham, N. J., assignor t Bell Telephone Laboratories, Incorporated, New r York, N. Y., a corporation of New York r a Application December 1, 1950, Serial No. 198,619

2 Claims. 1

This invention relates to telephone transmitters and more particularly'to carbon granule transmitters of the type disclosed in the application Serial No. 783,324, filed October 31-, 1947 of H. W. Bryant now Patent 2,532,694, granted December 5, 1950.

In general, a carbon ranule transmitter unit is composed of a chamber containing carbon granules, the chamber being defined in part by a pair of electrodes, one of which is fixed and the other of which is free to move with a diaphragm in accordance with sound waves effective thereon. The functioning of such units is dependent on the variation of the resistance of the current path through the carbon granules in accordance with the vibrations of the diaphragm.

The performance characteristics of such transmitters depend upon among other things the shape and spacing of the electrodes and the relative position of the instrument with respect to the gravitational field to which the instrument is subjected.

In some telephone systems, it is important that the agitated or talking resistance of a transmitter be uniform with respect to the space orientation of the instrument, especially where automatic line length equalizers which depend upon the current in the circuit are employed. Also, it is desirable that the maximum resistance to which a transmitter can be shaken or shocked under normal usage be minimized, since the maintenance .of the switchboard lamp light and the maximum distance to which a subscriber installation can be reached depend upon, among other things, the total circuit resistance of which the transmitter resistance is a part. Thus, a substantial reduction in the maximum transmitter resistance permits a longer extension of the transmission line from a signalling standpoint. A minimization of'the increase in this resistance inherent in the usage and aging the instrument is obviously advantageous.

- One object of this invention isto improve the performance characteristics of transmitters of the carbon granule type. More specifically one object of this invention is to minimize the effect of a variation in the angular position of the transmitter with respect to the gravitational field to which the instrument is subjected upon ithe performance characteristics of the transmit- Another object of this invention is to reduce the rate of increase of transmitter resistance with aging and usage.

In one illustrative embodiment of this invenface, coupled to adiaphragmto vibrate therewith, referred to hereinaftenas the vibratile electrode. I.

In accordance with one feature of this invention, the surface of the fixed electrode has a frusto-conical portion similar to that in the device disclosed in the application hereinabove and an annular portion, specificallypa portion generated by rotating a quarter circle about an-axis, at the larger base of the "frusto coni'calportion. The annular portion improves the positional per-- formance characteristics of theinstrum'ent.

The invention and the above n'ote'd and other features thereof will be understoodmore' clearly and fully from'the following detailed description with reference to the accompanying drawing in which: I f

Fig. 1 is an elevational view'in section of a transmitter illustrativeof' one embodiment of this invention;

Fig. 2 is a fragmentary, ct rial elevational view of the transmitterof f a Fig. 3 is a fragmentary sectional v'iew'fof th'e fixed electrode of the transmittr of Fig. 1 h

Fig. 4 is a graph comparingthe' talking resistance as a function of' space"orientation of the transmitter of Fig. "l with"a typical 'prior art transmitter; and

Fig. 5 is a fragmentary, sectional; elevational view of a transmitter illustrative"of'another em-.

bodiment of this invention. I

Referring now to t he drawing, the transmitter of Figs. 1, 2, and 3 comprises a foundationmemher or frame In, 'e'.-g., of metaLhavingan internal which the peripheral portidn l'3 of the diaphragm is seated. In addition to' 'the'peripheral portion l3, the diaphragm includes an annular portion l4 and a frusto-conical central portion l5 which is provided with reinforcing corrugations or flutes I6. Seated on the peripheral portion l3 of the diaphragm and secured to the frame [0 by the clamping band I 1 are a moisture resistant screen or membrane l8 and a multiapertured protective cap or cover l9.

An electrode 20, having a cylindrical portion 2|, a flange 22, tabs 23 and a substantially hemispherical portion 24, is aflixed centrally to and vibratile with the diaphragm, the inner edge of the diaphragm being clamped, with a metallic In addition to the peripheral flange portion an, I

the inner surface of the fixed electrode 3| comprises the bounding wall of a cylindrical aperture 33, a frusto-conical portion 34 andan annular portion 35. The annular portion, particularly advantageously, is a surface generated by revolving a quarter circle, one bounding radius of 4 signaling resistance of the transmitter disclosed in the aforeidentified application.

It has been found that with the fixed electrode contour of the present invention, the increase in the maximum unagitated transmitter resistance due to aging and usage is substantially reduced. Under conditions simulating extensive use in service, the resistance of the transmitter disclosed in the application aboveidentified increased essentially fifty-nine per cent (59%), while the resistance of a transmitter constructed in accordance. with the present invention increased only forty per cent (40%) when subjected to the same conditions.

In another embodiment of the present invention the back electrode 4|, shown in Fig. 5, in-

- cludes a cylindrical portion 42, interjacent the which is parallel to the axis of symmetry of the fixed electrode, about the axis of the fixed elect ode. the quarter circle and the axis. both. yin in the sein plane With reier noe o F .3, the dimensions of; the i. or surface of on spee fio embodiment of this iyention. ar

' R=0.1I7- inch r=0.020 inch 1 a=.085R inch b=.o4R inch c=-1.20 nch 7 After the cham er .0! bounded y the i ra e ec rode 2.0,, the flexible closur m m er 2 an the fix d electro e 3!, is filled. throug he yl ndrical ap rture .3 w th carb n granules o oth r comminuted resistance varying ma erial a cap 36 is crimped. o erthe fixe e ectr e 3!- When. a transmitter is held he face dow p s ti n as sh w F g. 1 the earths ra t tional fi ld t nds to pull th ca b n. ranu e other comminuted. resistance a yi g m t ia away rom. the fixed electrode a d the ta king resistance of a transmitter, such as the one disl sed in. the her tof e identified. pp icati n. increases as is shown by c rve A in Fi 4.. 1 n. accordance with a feature of the present invention, the carbon. granules or other comminut d r s sta c a y mat rial is intercept d in its a tempt .to flow out or the intere eotr cl r g on, Y y al ing a ainst the substantial y ver ic porti n 31. of theannular portion-i of th iixed el c r de 3 1, where y the contact pres ur f'the c r on gr nules or comm nu ed resistance ar ing, material in the region Z is increased; This r sults in a decrease n the talkin resistan e i the ac down position asis sh wn by curv B inFig.4. 5" i As shown in Fig. i, there i a eduction th a r t lking resistance of.- the transmitter lue to t e in re sed fixed elec rode are It was also o served that the init al s nalin resistan'c of the transmitter of this invention is su stan i lly eighte n per cent l8%)'l.ower han e i ial frusto-conical portion 44 and the annular portion 45.

Although specific embodiments of this invention have been shown and described, it will be understood that they are butillustrative and that vari= ous m difications can be mad h r Without departing from the scope and spirit of the in-. vention as defined by the appended claims What is claimed is:

A telephon transmitter comprising a fix and vibratile electrode having juxtaposed dished surfaces, one of which is convex and substantially hemispherical and the other of which is concave and frustoeconic'al with an annularportio'n'at the larger base of the frusto-conical portion, said an, nular portion being a surface of revolution the generatrix of which has a portion near the said frusto-conical portion and substantially parallel to the axis thereof, intersects the .trace of said frusto-conical portion in a cusp, and is a smooth convex curve, means including said surfaces bounding a chamber, and comminuted resistance varying material in said chamber.

2. A telephone transmitter comprising a fixed electrode and a vibratile electrode having juxtaposed dished surfaces, one of which is convex and substantially hemispherical and the other of which is concave and frustosconical with an annular portion at the larger base of the frustoconical portion, said annular portion being a segmentary torus and having a -portion essentially parallel to the direction of motion of the vibratile electrode and adjacent the'fr-u'sto-conical portion, means including said surfaces defining a chamber, and comminuted resistance varying material in said chamber.

HERBERT W. BRYANT.

REFERENCES CITED The following references ar e of the file of this patent:

UN T D TATE PA EN i Date 

